1. Field of the Invention
The present invention pertains to an overcast sewing machine for forming multiple-thread overcast seams, the sewing machine including at least two thread-carrying needles arranged at spaced locations from each other, one thread carrying lower looper taking up and throwing off the needle thread loops, and one thread-carrying overcast looper arranged on a looper holder for taking up the looper thread carried by the needle thread loops and laying the overcast looper thread around the edge of the material being sewn and feeding it for inserting the needles into a triangle formed by the leg of the overcast looper thread extending from the thread eye to the interlacing of the lower looper thread with the overcast looper thread at the edge of the material being sewed, by the needle-side leg of the lower looper thread line around the overcast looper, and by the overcast looper and, to an improvement of the design according to West German Offenlegungsschrift No., DE-OS36,36,390.
2. Background Art
The West German Offenlegungsschrift No., DE-OS 36, 39,390 discloses an overcast sewing machine with at least three thread-carrying needles, which are arranged next to each other, are aligned in a straight direction at right angles to the direction of feed of the material to be sewn and are arranged in a needle holder from which one needle or more needles can be removed. The sewing machine includes a thread-carrying lower looper, which cooperates with all needles; and an overcast looper, to which a limited pivoting movement is imparted, and which cooperates with all the needles except for the needle located farthest away from the edge of the material to be sewn.
This overcast sewing machine forms an overcast stitch type not covered by either U.S. Federal Standard Catalogue No. 751 or German DIN Specification No. 61400, which consists of at least five threads, including three needle threads, which penetrate the material being sewn during sewing and are subdivided, depending on the distance from the edge of the material being sewn, into first needle threads and one last needle thread, as well as one lower looper thread and one overcast looper thread, which are interlaced at the edge of the material being sewn and are interlinked with all needle threads in the material being sewn. The overcast looper thread extends between the lower looper thread, with which it is interlinked at the edge of the material being sewn, and the first needle threads, which extend in parallel to the edge of the material being sewn and next to each other at spaced locations, and all of them are interlinked with the overcast looper thread. However, the last needle thread is interlinked only with the lower looper thread.
By inserting another thread-carrying needle in the needle holder, it is possible to make a stitch type consisting of six threads, namely, four needle threads, one lower looper thread, and one overcast looper thread, in which stitch type the needle thread located farthest away from the edge of the material being sewn is interlinked only with the lower looper thread, and all others are interlinked with the lower looper thread and the overcast looper thread.
If sewing is performed with only two thread-carrying needles, stitch type 514 is formed, which consists of two needle threads, one lower looper thread, and one overcast looper thread, and the latter is interlinked with both needle threads in the fabric being sewn and is interlaced with the lower looper thread at the edge of the material being sewn.
To form stitch type 504, which consists of one needle thread, one lower looper thread, and one overcast looper thread, which are interlaced with each other at the edge of the material being sewn and are interlinked with the needle thread in the material being sewn, the second needle must be removed.
If, among the three thread-carrying needles, the needle located farthest away from the edge of the material being sewn is retained, and the first or second needle is optionally removed, it is possible to form stitch type 512, in which the needle thread located farthest away from the edge of the material being sewn is interlinked only with the lower looper thread in the material being sewn, while the lower looper thread and the overcast looper thread are interlinked with the other needle thread in the material being sewn, and the latter threads are interlaced with each other at the edge of the material being sewn.
The changeover from one stitch type to another is consequently carried out by adding or removing certain needles. Even though it is thus possible to make several stitch types on one sewing machine, when adding one or several needles, it is necessary to rethread the needle thread, usually through a number of thread guide eyes and the eye of the needle, which is relatively time-consuming, in addition to insertion into the needle holder and fixing.